The Hawaiian archipelago was formed by volcanic activity, and many of the state's volcanoes remain active. The Kilauea Volcano in Hawaii Volcanoes National Park on the Big Island glows under a starry sky. Getty Images/iStockphoto

Hawaii Volcanoes National Park is one of seven national parks in the state and one of the most popular. It's one of the few places in the world where you can witness volcanic action firsthand. Tor Johnson, Hawaii Tourism Authority

Hawaii's volcanic geology means that many of the island's beaches are covered in black sand. Punaluu Black Sand Beach on Hawaii's Kua coast is one of the most famous. Tor Johnson, Hawaii Tourism Authority

Haleakala National Park on the island of Maui is home to the island's highest peak of the same name, jutting 10,023 feet above sea level. Many visitors wake up early to catch a sunset from the summit of the volcanic peak. Getty Images/iStockphoto

Kauai, the oldest of Hawaii's main islands, is a land of lush valleys, soaring cliffs and cascading waterfalls. Manawaiopuna Falls, one of the most spectacular, is typically reached by helicopter. Getty Images/Zoonar RF

Hawaii isn't typically associated with snow, but when you head to the top of Mauna Kea -- the world's tallest mountain if measured from the ocean floor -- you might find some. It's home to the world's biggest telescope and is a favorite locale among star gazers. Getty Images/iStockphoto

The island of Lanai remains one of Hawaii's most pristine inhabited islands -- home to some of the state's best beaches and natural scenery, like the Kaholo Cliffs. Pierce M Myers Photography/Hawaii Tourism Authority

Not all of Hawaii's activities involve the water. The Kalalau trail on Kauai often ranks among the world's most beautiful hiking trails, but it's also one of the most dangerous. Getty Images/iStockphoto

Those who brave the 11-mile Kalalau trail beginning at Kee Beach (pictured), with its crumbly trail bed and sheer drop-offs, are rewarded with the chance to experience one of the state's most remote stretches of sand, Kalalua Beach. Getty Images/iStockphoto

Hawaii is one of the nation's most multicultural states. The state's Asian heritage can be seen at The Great Buddha statue at Lahaina on Maui -- the largest Buddha statue of its kind outside of Japan. Getty Images/iStockphoto

Kohola is the Hawaiian word for humpback whale, and an estimated two thirds of the Northern Pacific humpback whale population come to the waters of Hawaii to breed and raise their young. Getty Images/iStockphoto

Even when it's not whale season, the waters off Hawaii's islands teem with life. Some of the state's best diving and snorkeling can be found in Molokini crater, a crescent-shaped marine sanctuary off the coast of Maui. Getty Images

The seven-mile-long stretch of sand known as Polihale sits within Polihale State Park on the island of Kauai. Journeying to the beach via a bumpy dirt road is worth it for the sunset views alone. Flickr/Justin Ornellas

Hawaii Island, also called the Big Island, is the state's youngest, largest and still-growing island. On this island, you can laze on a beach and walk through the snow in a single day. Getty Images/iStockphoto

Anyone who's seen the hit TV series "Lost" will recognize Mokuleia Beach Park in North Shore, Oahu. The beaches here are remote enough that you could easily spend a day without seeing another human being. Getty Images/iStockphoto

For a road trip, island-style, hop in the car, turn on some tunes and drive the road to Hana -- a three hour drive from from Lahaina or Kihei with plenty to see and do along the way. Getty Images/iStockphoto

Surfing is believed to have originated in Polynesia and was once a sport of only Hawaiian royalty. Today, surfers from around the globe come to catch Hawaii's world-class waves. Kirk Lee Aeder, Hawaii Tourism Authority

Hawaii's cultural history dates back centuries, and you can learn about it at sites like Puukohola Heiau National Historic Site, a once sacred place of worship for native Hawaiians. Tor Johnson, Hawaii Tourism Authority

The Kealakekua Bay State Historical Park was the site of first significant contact between native Hawaiians and Westerners. Here, visitors can see kii, sacred carvings of deities or ancestral spirits. Tor Johnson, Hawaii Tourism Authority

Visiting Molokai is like stepping back in time. One of the island's most charming experiences occurs each Friday night when the island's elders gather for an evening of live music and hula at Hotel Molokai. Dana Edmunds, Hawaii Tourism Authority

Parts of Lanai Island, like Keahiakawelo, have an almost lunar landscape, in contrast to Hawaii's typically lush terrain. Which picture most makes you want to travel to Hawaii? Dana Edmunds, Hawaii Tourism Authority

The problem: The airline needs to complete the Federal Aviation Administration's certification process for extended overwater flights, but the FAA workers who oversee those so-called ETOPS activities are on furlough.

Southwest received key ETOPS approvals before the shutdown, covering its manuals and proposed procedures, but the final steps, including "validation'' flights, remain.

Southwest spokesman Brian Parrish said the airline continues to prepare for Hawaii internally but can't complete the process until the required FAA employees are back on the job.

"We are ready to continue the ETOPS application process when the FAA is allowed to resume full certification activities,'' the airline said in a statement Monday.

Southwest had hoped to start selling tickets to Hawaii in late 2018, with flights debuting in early 2019. Airline executives have said they can begin selling tickets and launching the flights as soon as they receive ETOPS certification.

Southwest still is waiting for the ETOPS authorization it needs for Hawaii flights.(Photo: Southwest Airlines)

Southwest CEO Gary Kelly said in late October that the airline will start selling tickets "within days'' of receiving certification, with the first Southwest flights to Hawaii launched within weeks of that.

Travelers hoarding Southwest frequent flier points for the Hawaii flights pepper the airline daily with questions on the timing of the Hawaii flights. The airline has not revealed any Hawaii schedule. It has only said that it will initially fly to Hawaii from four California cities: San Diego, Sacramento, Oakland and San Jose. It will fly to four destinations in Hawaii.

Lava has been visible at Hawaii Volcanoes National Park for years. But in recent weeks, volcanic activity has subsided significantly -- so much so that for the first time in a long time, there is no molten lava to see at Hawaii Volcanoes National Park. Getty Images/iStockphoto